1. Field of the Invention
This invention relates to a sintered alumina-based composite body having high strength and high toughness and also to a process for producing such a sintered, high-strength and high-toughness, alumina-based composite body by controlling its structure.
2. Description of the Prior Art
Addition of various whiskers, fibers or the like is generally practiced to obtain ceramic materials having high strength and high toughness. When a sintered composite body is obtained by adding whiskers, fibers or the like to a raw batch and then firing the resultant mix, it is however difficult to obtain the sintered composite body in a densified form, that is, to impart high strength and high toughness to the sintered composite body.
Japanese Patent Application Laid-Open (Kokai) No. 62-72522 and Japanese Patent Publication (Kokoku) No. 4-24305, on the other hand, disclose a composite alumina-titania powder and a sintered corundum-rutile composite body composed of a corundum-phase alumina and a rutile-phase titania. Sintered bodies of the above composite powder and the sintered composite bodies show higher toughness compared with sintered bodies formed of a single corundum-alumina phase.
The sintered corundum-titania bodies disclosed in the above publications are however accompanied by the problems that temperature control is difficult upon sintering and, when the temperature is raised in an attempt to achieve further densification of the sintered bodies, the whole structure is converted to a plate-like or rod-like structure and no higher toughness cannot be achieved.
According to the above production process, a sintered body of a mixed structure is produced by first preparing a mixture of uniformly dispersed alumina and additives, forming (shaping) the mixture into a green body and then firing the green body. The above production process is therefore accompanied by the problem that free control of the structure can hardly be achieved.